Are juveniles of the enigmatic deep-sea nematode Rhaptothyreus (Rhaptothyreida: Rhaptothyreidae) parasitic?

  • Rhaptothyreus is arguably the most enigmatic nematode taxon due to a combination of unusual morphological features (e.g., large feather-like amphids, vestigial mouth, trophosome, single spicule), unclear phylogenetic relationships (possible affinities with the Enoplida, Mermithida and Benthimermithida) and a distribution restricted to the deep sea. Here I provide the first record of the genus in the Western Pacific Ocean and describe new morphological features of a moulting juvenile. This specimen is characterised by features that differ markedly from those of the adults, the most prominent being the absence of cephalic sensillae and amphids and the presence of a stylet-like structure in the buccal cavity. Similar contrasts in morphology are found between adults and juveniles of the order Benthimermithida, which is characterised by free-living adults and parasitic juveniles. Other morphological (large body size, presence of trophosome) and distributional characteristics (predominantly deep-sea distribution, juveniles rare / absent in sediments) are also common to both groups. Published records show that Rhaptothyreus is commonly found in oligotrophic environments (e.g., abyssal plain) where organisms bearing symbiotic bacteria are not typically found, which makes the presence of endosymbiotic bacteria inside the trophosome unlikely. These observations are consistent with the existence of a parasitic juvenile life stage in Rhaptothyreus.

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Author:Daniel LeducORCiD
Parent Title (English):European journal of taxonomy : 94
Series (Serial Number):European journal of taxonomy : EJT (94)
Publisher:Muséum National d'Histoire Naturelle
Place of publication:Paris
Document Type:Part of Periodical
Year of Completion:2014
Year of first Publication:2014
Publishing Institution:Universitätsbibliothek Johann Christian Senckenberg
Release Date:2016/06/28
Tag:Benthimermithida; New Zealand; Rhaptothyreus typicus; continental slope; ontogeny
Page Number:12
Dewey Decimal Classification:5 Naturwissenschaften und Mathematik / 59 Tiere (Zoologie) / 590 Tiere (Zoologie)
Sammlungen:Sammlung Biologie / Sondersammelgebiets-Volltexte
Licence (German):License LogoCreative Commons - Namensnennung 3.0